This randomized controlled clinical trial aims to evaluate the antibacterial efficacy and stability of strontium-incorporated hydroxyapatite (Sr-HA) coated orthodontic mini-screws (OMSs) used for maxillary canine retraction. A double-blind, split-mouth design was employed, involving 20 patients (aged 16-20 years), each receiving two titanium alloy mini-screws (1.6 mm × 8 mm): one coated with Sr-HA (5% concentration via electrochemical deposition) and one uncoated control. A total of 40 mini-screws were assessed. Following upper first premolar extractions, canine retraction was initiated using 150 g NiTi coil springs on 17×25 SS archwires. Mini-screws were placed between the upper second premolar and first molar without flap elevation or pilot hole drilling. Parameters including screw stability, antimicrobial activity, and gingival blood flow were monitored over a 4-month period. The incorporation of Sr-HA is hypothesized to enhance mini-screw osseointegration, reduce peri-implant inflammation, and improve clinical outcomes by leveraging the osteogenic and antibacterial properties of strontium. This study aims to provide evidence supporting the use of Sr-HA coatings to reduce mini-screw failure rates in orthodontic treatment.

Aim of the study:

The aim of this study is to evaluate the antibacterial efficacy and stability of strontium- incorporated hydroxyapatite (Sr-HA) coated orthodontic mini- screws used in maxillary canine retraction in comparison to uncoated mini- screws.

Material and methods:

1. All patients will be treatment with fixed appliance and Roth type brackets where leveling and alignment will be done utilizing nickel titanium.
2. Extraction the upper first premolars and retraction the canine will be done using 17 ×25 SS wire.
3. A periapical X-ray will be taken to confirm the mini screw position to avoid interference with adjacent root and to ensure that there are no periapical lesion.
4. Symmetrical orthodontic miniscrews will be inserted between the second premolar and first molar.
5. The OMSs that will be used in this study will be self-drilling, conical in shape, 1.6 mm in diameter, and 8 mm in length, constructed of titanium alloy, i well be purchased from Dentaurum company [Germany].
6. The orthodontic main screws were loaded with a 150 g NiTi coil spring.
7. On one side, a coated will be inserted, and on the other side, an uncoated will be used for the same patient.
8. Coated materials will utilize [Strontium incorporated hydroxyapatite] applied by electrochemical deposition and concentration percentage about 5 % .
9. No mucoperiosteal flap will be raised, and no pilot hole will be made during the procedure.
10. Will be assessed throughout follow-up periods of up to four months.

Outcome Measurement:

1. Assessment Orthodontic mini-screws stability (coated and uncoated) using Periotest device .
2. Evaluate antimicrobial effect of Strontium incorporated Hydroxyapatite using Enzem- Linked Immunosorbent technique .
3. Evaluate blood flow by periodental probe.
4. Gingival health by visual assessment .

Inclusion Criteria:

1. Adult patients within an age range (16-20) years.
2. Orthodontic treatment plan requiring the extraction of the upper first premolars.
3. Patients have fully permanent teeth are erupted (third molars are not included).
4. No previous orthodontic treatment
5. No medical problem that could interfere with treatment.

Exclusion Criteria:

1. Presence of problematic healing such as, compromised immune defense, bleeding disorder, pathological bone quality, and xerostomia.
2. Inadequate oral hygiene.
3. Heavy smoking

individual participants available upon request